1. Field of the Invention
The present invention relates to a substrate processing apparatus for performing a resist coating process on semiconductor substrates, glass substrates for liquid crystal displays, glass substrates for photomasks, substrates for optical disks or the like (hereinafter briefly referred to as “substrates”) transferred out of an indexer in a predetermined order as well as performing a development process on the substrates once transported to the outside of the apparatus to undergo an exposure process and then transported back into the apparatus and returning the substrates to the indexer. More particularly, the present invention relates to a substrate processing apparatus for making inspections at inspection units on substrates having undergone the development process.
2. Description of the Background Art
As is well known, products such as semiconductors and liquid crystal displays are manufactured by performing a series of processes including cleaning, resist coating, exposure, development, etching, formation of interlayer dielectric films, thermal processing, dicing and the like, on the above-described substrates. Widely used as a so-called coater/developer is a substrate processing apparatus in which a plurality of processing units for performing, for example, among the series of processes, resist coating, development and their associated thermal processes, respectively, are incorporated, and transport robots circularly transport substrates between the respective processing units, so that the substrates are subjected to a series of photolithography processes.
Recently, such substrate processing apparatus is equipped with inspection units for making various kinds of inspections on substrates for quality verification in order to maintain the quality of semiconductor products or the like, as proposed in Japanese Patent Application Laid-Open Nos. 2000-223401, 2002-151403 and 2003-209154, for example. For instance, a substrate processing apparatus includes a film thickness measurement unit for measuring the film thickness of a substrate with a resist film formed thereon and a line width measurement unit for measuring the line width of a pattern after the development process is performed.
In the above-described substrate processing apparatus, substrates are subjected to a series of photolithography processes in the order transferred out of an indexer which takes out a substrate from a carrier for storing unprocessed substrates and transfers the substrate outwardly to a processing unit. That is, a substrate transferred out of the indexer later is prohibited from passing a preceding substrate transferred out of the indexer earlier during a series of processes. This is because processing uniformity among a plurality of substrates should be ensured and because allowing such passing will extremely complicate a program for transport control.
On the other hand, in a substrate processing apparatus equipped with inspection units, inspections are generally made on some of substrates at random, not on all substrates subjected to processing (i.e., so-called sampling inspection). It is not necessary to transport substrates not to be inspected (hereinafter also referred to as non-inspected substrates) to the inspection units, however, such non-inspected substrates are transported to the inspection units in accordance with a predetermined transport order and are taken out from the inspection units after a lapse of a predetermined time period without making any inspection because substrates have conventionally been prohibited from passing preceding substrates. Such transport without any processing degrades the transport efficiency of the apparatus as a whole, resulting in a decrease in throughput.